In the textile industry, it is common practice to apply textile dyes and finishing chemicals to cotton and cotton polyester woven fabrics to impart color and to enhance comfort and ease of care of the fabrics in use. The goods are prepared by known procedures such as de-sizing, bleaching and/or mercerizing. After the preparation stage, the goods are dried prior to dyeing or finishing. If the goods are dyed, they will also be subsequently dried and then finished.
A textile fabric is normally rewet with water after it leaves the preparation stage and then is squeezed with rubber squeeze rolls prior to drying. Upon exiting the squeeze rolls, the percentage of moisture in the fabric will vary from 50 percent for blends including 65 percent polyester and 35 percent cotton to 75 percent for 100 percent cotton fabrics.
Analysis has indicated that the moisture content of the fabric exiting the squeeze rolls can be lowered to 16-25 percent on a blend of 65 percent polyester and 35 percent cotton and 40-55 percent on a 100 percent cotton fabric. Most ranges run some blends and, thus, the average energy reduction is 50 percent. The average energy cost is approximately $80,000 per year per range resulting in a $40,000 yearly energy savings.
Currently, chemicals are applied in approximately a 5-10 percent solution by dipping the dry fabric in the solution and squeezing with rubber squeeze rolls. The moisture content of the fabric exiting from the squeeze roll varies from 50 percent for a fabric blend of 65 percent polyester and 35 percent cotton to 75 percent for 100 percent cotton fabric. This moisture content can vary plus or minus 10 percent side-to-side due to uneven squeezing caused either by uneven pressure or rubber roll wear. In addition, some solution is left between the woven threads in a "window pane" effect.
Fabric construction, the intended use of the fabric, and whether it is a 100 percent cotton material or a blend will effect the make-up of the chemical solution applied to the fabric. It is desirable to run as many styles as possible with one chemical solution in order to maximize production efficiency and to minimize down time effect.
There has been considerable analysis and testing done in connection with the various fabrics. The results show that the percentage of moisture in the fabric as it leaves the vacuum slot depends primarily on the polyester content, varying from 16 percent for a blend including a 70 percent polyester and 30 percent cotton to 45 percent for a 100 percent cotton fabric. There is some variance between different styles of a blend due to differences in the weave, permeability and distribution of the two different fibers.
It is known in the industry that use of vacuum systems to apply finished chemicals will produce some chemical savings. However, there are some difficulties encountered in the bare application of a vacuum system to the different variety of fabrics being treated. It has been found, for example, that using existing vacuum systems on blends of 65 percent polyester to 35 percent cotton will cause a variation from 18 to 35 percent in moisture level depending on the style permeability with the vacuums fluctuating between 15 and 4 inches of mercury. The moisture level in the fabric as it exits from the point where vacuum is applied will gradually increase during the run as the conventional type of air and liquid separator has its strainer coated with lint. The vacuum fluctuation is primarily due to differences in fabric permeability. The typical vacuum systems do not produce enough air on the open fabrics resulting in a decrease in vacuum. Thus, the mill is forced to frequently change chemical concentrations or to put on higher concentrations to take into account these inconsistencies. The result is a significant reduction in the amount of saved chemical.
Accordingly, while there is no question that the use of vacuum is a valuable tool in the dewatering of fabrics and in treating the fabrics with desirable chemical treatment, there is still room for further improvement. This is true in regard to controlling the moisture level in the deliquefying processes for polyester and cotton blends and for all cotton fabrics in particular. In addition to the consistency and control over the moisture level in the fabric as it is deliquefied, chemically treated and deliquefied again, it is also desirable to provide savings in the necessary chemicals utilized in the process to the greatest possible degree. Moisture control and greater savings in chemicals are consistently desired. This is particularly true in industrial environments where cost is a significant factor in regard to materials, energy, and the close control over the process for dependability and reproducibility over an extended period of time.